Here's why:

* Ozone Depletion Potential (ODP): CFCs have a very high Ozone Depletion Potential (ODP). This means they are extremely effective at breaking down ozone molecules in the stratosphere.

* Long Lifespan: CFCs are very stable and can persist in the atmosphere for decades, continuing to destroy ozone during that time.

* Global Impact: The use of CFCs was widespread, leading to a significant depletion of the ozone layer, which protects us from harmful ultraviolet radiation from the sun.

Other gases that contribute to ozone depletion include:

* Halons: These are similar to CFCs and were used in fire extinguishers.

* Methyl bromide: Used as a fumigant.

* Hydrochlorofluorocarbons (HCFCs): These were developed as replacements for CFCs, but they also have ozone-depleting properties.

Important Note: The Montreal Protocol, an international treaty, has phased out the production of ozone-depleting substances like CFCs. This has led to a gradual recovery of the ozone layer.